The human body is made of about 200 joints. The bones meet each other in the joints, which are composed of cartilage, joint capsule, synovial membrane, ligament, tendon, muscle, etc. in order to smoothly move between the bones and play a role in absorbing the impact caused by the movement.
Inflammatory diseases that occur in these joints can be divided largely into chronic rheumatoid arthritis, which is understood to be caused by autoimmunity, infectious arthritis caused by bacterial infection, deformed arthritis caused by degeneration or destruction of articular cartilage or bone due to various causes, and crystalline arthritis caused by deposition of soluble metabolites as crystals in the connective tissue around the joints due to degenerative changes of the connective tissue.
Degenerative arthritis, that is, osteoarthritis, is a disease caused by the destruction of joint tissue due to the increases of synthesis and activity of matrix metalloproteinase (MMP), which degrades the joint matrix in joint cells by the production of inflammatory cytokines, such as, interleukin-1β and tumor necrosis factor-α, while the degeneration of chondrocytes forming joints occurs due to aging, thereby inhibiting the synthesis of type II collagen and proteoglycan, which are matrix materials of joints in chondrocytes.
Further, the arthritis is worsened by the production of nitric oxide because of inflammatory cytokines and by the production of self-amplifying cytokines due to the produced nitric oxide, which leads to the synthesis of more MMPs and promotes the degradation of the joint matrix. At the same time, inflammatory cytokines increase the production of prostaglandin E2 that is a lipid metabolite, and thus, lead to an inflammatory response in arthritis.
Various biochemical phenomena are involved in the inflammatory reaction in vivo. Particularly, the inflammatory reaction is initiated or adjusted by various enzymes, which are related to the inflammatory response produced by immune cells. Specifically, the immune cells migrate to the injured site through the blood vessels with the help of histamine, nitric oxide (NO), prostaglandin E2 (PGE2), etc., and then, begin the inflammatory reaction. The immune cells migrated to the injured site secret cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), or interleukin-6 (IL-6) or chemokines such as MIP-1, IL-8, or MCP-1 to destroy direct external invaders or collect other immune cells, thereby initiating the inflammatory response.
In the case where being exposed to inflammatory-inducing substances such as interferon-λ, lipoteichoic acid, and lipopolysaccharide (LPS), which induces the inflammatory reaction, or various inflammation-inducing cytokines, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2(COX-2) are expressed, thereby producing the excess NO and PGE2. The several inflammatory initiators (iNOS, COX-2, TNF-α, IL-6, etc.) promote transcription by activated NF-κB, so that NO is produced more than was needed, thereby causing vasodilation due to shock, tissue damage caused by inflammatory response, mutagenesis, damage of nerve tissue, and the like.
Nitric oxide (NO) is produced from L-arginine and molecular oxygen by NO synthase (NOS). In mammals, there are three types of NOS: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). nNOS and eNOS are constitutively expressed in nerve cells and endothelial cells. However, iNOS is inductively produced in macrophages or monocytes by exposure to LPS-induced or pro-inflammatory cytokines (Vane et al., 1994). NO produced in iNOS causes inflammation or an immune response, and thus acts as a proliferation inhibitor or a cytotoxic agent of a pathogen that invades the cell. However, it is known that excess NO produced by overexpression of iNOS causes pathological conditions (Kim et al., 2005; Pan et al., 2011). The deleterious effect of excess NO in the cell not only acts as an inflammatory mediator itself, but also reacts with superoxide to produce peroxynitrite. Peroxynitrite may not only cause oxidative damage of intracellular molecules such as proteins, fats and DNA, but also modify normal gene regulation. Thus, overexpression of iNOS as well as large amounts of NO is closely related to pathological conditions associated with various inflammatory diseases (MacMicking et al., 1997; Maeda and Akaike, 1998).
Nuclear factor kappa B (NF-κB) plays a major role in immune and acute inflammatory responses as well as cell growth (Li and Verma, 2002; Makarov, 2001). NF-κB activation promotes the expressions of iNOS and several pro-inflammatory genes (Kim et al., 2005; Makarov, 2001). The activation pathway of NF-κB is such that the inhibitor of κB (IκB)-α kinase is phosphorylated by LPS followed by phosphorylation of IκB-α, and IκB-α phosphorylated by ubiquitin is degraded to cause free NF-κB to move the nucleus, thereby adjust inflammatory related genes (Chen et al., 1995). Activation of another NF-κB occurs via mitogen-activated protein kinases (MAPKs) (Guha and Mackman, 2001) or phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway (Sheu et al., 2005). MAPKs have extracellular signal-regulated kinases (ERKs), c-Jun NH2-terminal kinases (JNKs), and p38 MAPKs, which are involved in transcriptional regulation of inflammatory genes through NF-κB activation (Bhat et al., 1998; Kao et al., 2005; Shin et al., 2010). PI3K is also involved in the production of inflammatory cytokines through NF-κB activation (Cremer et al., 2011; Sheu et al., 2005). PI3K activation phosphorylates the phosphatidylinositide to activate the Akt protein. The activated PI3K/Akt plays a major role in the activation of macrophages (MacMicking et al., 1997; Sheu et al., 2005). Therefore, in order to develop an anti-inflammatory agent, many studies have been carried out to find a substance that inhibits the activation of NK-κB or inhibits activation of MAPKs and Akt which activate NF-κB.
MMPs are proteolytic enzymes that destroy bone and cartilage matrix components and are expressed in cartilage tissues stimulated by inflammatory cytokines in inflammatory disease states, resulting in increased activity. MMPs constitute at least 21 enzymes, being classified into subclasses including collagenase (MMP-1, 8, and 13), stromelysin (MMP-3, 10, and 11), gelatinase (MMP-2 and 9), and matrix type-1 metalloproteinase (MMP-14). Among them, MMP-2 and MMP-9 are gelatinase subfamily, which is an important enzyme for collagen degradation of cartilage tissue. These two enzymes break down other substrates, such as fibrous collagen I and II, which are abundant in cartilage, and aggrecan.
Rheumatoid and degenerative arthritis are characterized by inflammatory cell infiltration into synovial tissue, which is mediated by chemokines. It is known that chemokines such as monocyte chemoattractant protein-1 (MCP-1) are expressed in the synovial tissue, and they are produced in synovial fibroblasts and the like. Excessive MCP-1, produced by arthritis, causes monocytes and macrophages to come in inflammatory sites and activates these cells to promote the production of inflammatory cytokines, thereby further aggravating the inflammation.
The expression of adhesion molecules such as vascular cellular adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), and E-selectin in vascular endothelial cells was increased by cytokines in synovial tissues of rheumatoid and degenerative arthritis to induce infiltration of inflammatory cells. Overexpressed ICAM-1 and VCAM-1 are associated with chronic inflammation such as rheumatoid arthritis and degenerative arthritis.
Rheumatoid and degenerative arthritis are chronic systemic inflammatory diseases that cause symmetrical, multiple arthritis, resulting in joint damage and deformation. In the absence of treatment for these arthritis, the progression is poor, indicating a disability of the joint function, and if persistent, disability of the joint function interferes with daily life. In Korea, it is estimated that about 1% of the total population is suffering from rheumatoid arthritis. It is known that the incidence ratio of rheumatoid arthritis is three times higher in women than in men, and it occurs mainly in the 20s and 40s.
The main causes of rheumatoid arthritis have been increasingly revealed, and genetic factors, infections, hormonal abnormalities, etc. are thought to be causative factors. Because of these causative factors, “autoimmune” phenomenon occurs. The autoimmune is a phenomenon that chronic inflammation occurs multiply and lastingly in many parts of the body due to abnormality of immune regulation function of our body.
Meanwhile, drugs used in the treatment of arthritis can be categorized on the basis of the main mechanism of action such as reduction of inflammation, delay of disease progression, and decrease of uric acid concentration. Many neuroarthritis treatment drugs act to reduce inflammation. Inflammation is a pathological process that causes pain, swelling, fever, seizures, and stiffness. Drugs that rapidly relieve inflammation include nonsteroidal anti-inflammatory drugs including aspirin and steroidal anti-inflammatory drugs including cortisone.
Nonsteroidal anti-inflammatory drugs have the effect of relaxing nerve joints and relieving inflammation by reduction of pain. However, because gastrointestinal disorders may occur or abdominal pain may be induced, use thereof is preventive for some people with active peptic ulcer or hemorrhagic lesions in the gastrointestinal portion. Steroidal anti-inflammatory drugs are not used well for degenerative arthritis due to severe side effects such as weight gain and hypertension compared to their effects.
In particular, steroidal anti-inflammatory drugs have nothing to do with the causative treatment of the disease, and may simply induce excessive use of joints by temporarily reducing the pain, which causes destruction of the nerve joints and deterioration of the disorder so that it requires attention in use.
Therefore, conventional therapies used for joint damage such as arthritis have limited effectiveness, involve obvious toxic side effects, cannot be used continuously for a long period of time, and thus their effectiveness is limited. Thus, there is a desperate need for a novel therapeutic method or a therapeutic agent that overcomes the disadvantages of conventional therapeutic methods.